Addressing a rally on Saturday, he had said, “look at what’s happening last night in Sweden”, as he listed parts of Europe hit by terrorist attacks.
With no such incident reported in Sweden on Friday, the country asked the US administration for an explanation.
Mr Trump tweeted on Sunday that he had been referring to a TV report.
He said it had been broadcast on Fox News but did not say when. He may have been referring to a Fox News programme on Friday night, which looked at refugees and crime in Sweden.
Despite his words “happening last night in Sweden”, White House spokeswoman Sarah Huckabee Sanders said separately that Mr Trump had been talking about rising crime and recent incidents in general, not referring to a specific issue.
Former Swedish Prime Minister Carl Bildt was among those who mocked Mr Trump’s comment, suggesting that he had “been smoking”.
Sweden? Terror attack? What has he been smoking? Questions abound. https://t.co/XWgw8Fz7tj
— Carl Bildt (@carlbildt) February 19, 2017
Social media users ridiculed the American leader, joking about imaginary situations involving Swedish institutions like the pop group Abba and furniture store Ikea.
The mocking hashtag #lastnightinSweden was soon trending on Twitter.
Many made reference to the “Bowling Green massacre“, a non-existent attack cited by one of President Trump’s key advisers, Kellyanne Conway, earlier this month.
On Sunday, a librarian was in charge of Sweden’s national twitter account, @Sweden, which is run by a different Swedish resident every week.
It fell on her to field countless inquiries about Mr Trump’s remarks.
“I was just myself and told the truth,” she told BBC Radio 4’s Today Programme on Monday. “I am a school librarian as a profession, so I just went out and checked all the main newspapers in Sweden and radio channels, and I just concluded it was not true.”
What Trump said
On Sunday, Mr Trump tweeted: “My statement as to what’s happening in Sweden was in reference to a story that was broadcast on @FoxNews concerning immigrants & Sweden.”
The Fox News report looked at gun violence and rape in Sweden since it opened its doors to large numbers of asylum-seekers in 2013.
Fox News is known to be among Donald Trump’s favourite cable TV channels.
President Trump’s initial remarks about Sweden came at a big rally in Florida on Saturday.
“You look at what’s happening in Germany, you look at what’s happening last night in Sweden,” he said.
“Sweden, who would believe this? Sweden. They took in large numbers. They’re having problems like they never thought possible. You look at what’s happening in Brussels, you look at what’s happening all over the world. Take a look at Nice, take a look at Paris.”
What actually happened
No terrorist incidents were reported in Sweden on Friday.
Sweden’s Aftonbladet website summarised the news events of that day, which included:
- A man setting himself on fire at a plaza in central Stockholm.
- Famous singer Owe Thornqvist suffering technical problems in rehearsals
- A man killed in workplace accident
- Road closures in northern Sweden due to “harsh weather”
- A police car chase through central Stockholm after a suspected drunk driver
Sweden, with a population of about 9.5m, has taken in nearly 200,000 refugees and migrants in recent years – more per capita than any other European country.
It saw a sharp increase in asylum seekers in 2015, with more than 160,000 people arriving. With the influx, tensions also rose with some isolated attacks on immigrants, as well as pro- and anti-migrant demonstrations.
The killing of a 22-year-old woman in January 2016 by an asylum seeker based at the centre where she worked put further pressure on the government to reassess its approach to refugees.
There was a drop in numbers last year after the country introduced new border checks incurring longer processing times, as well as financial incentives for migrants who voluntarily returned to their country of origin.
No terrorist attacks have been recorded in Sweden since the country’s open-door policy on migration began in 2013.
However, Sweden is believed to have the highest number of Islamic State fighters per capita in Europe. About 140 of the 300 who went to Syria and Iraq have since returned, leaving the authorities to grapple with how best to reintegrate them into society.